Fact sheet number: FS-2001-02-35-MSFC
The idea that ordinary people could someday live and work in space for extended periods for time has fascinated science fiction fans as well as serious scientists and engineers.
But is living in space different from living on Earth? Is the human body designed to operate in gravity that is less than Earth's?
It is important for the success of long-duration space missions - such as a flight to Mars - for researchers to understand the sensory, motor and perceptual factors that influence a space crew member's ability to adapt to different gravitational forces. Life on the Space Station demands the need to evaluate the influence of microgravity on the coordination of complex body activities -- such as reaching, bending and balance - to better prepare the next generation of space travelers.
Researchers performed experiments on earlier Space Shuttle missions and on Skylab and Mir revealed that exposure to weightlessness causes changes in a person's neurovestibular system - changes related to the inner ear, equilibrium and awareness of body or limb orientation. They learned that when a space crewmember returns to Earth, the individual's microgravity-adapted neurovestibular system must readjust to a gravity environment. As a result, standing and walking, which require adequate balance, were temporarily affected.
In the H-Reflex experiment planned for Expedition Two of the International Space Station, researchers for the Canadian Space Agency are seeking additional information on changes to the human neurological system that occur during long-duration space flights.
Researchers already know prolonged weightlessness results in a loss of muscle strength and decreased bone density. Currently, the only known treatment for this problem is in-flight exercise. But does exercise work on a long space flight?
A goal of the H-Reflex experiment is to help researchers determine if exercise could be made more effective on long space flights.
The experiment measures spinal cord excitability - its ability to respond to stimuli. Researchers believe that spinal cord excitability decreases during prolonged space flight.
If this proves true, they hypothesize that in-flight exercise would be less effective and the space crews will have to work harder and longer to achieve any benefit. If spinal cord excitability does decrease on prolonged flights, researchers may be able to reverse the effect and lower the amount of exercise now required in space and thus increase space crewmember productivity during the flight.
In the experiment, a mild electrical shock will be applied to the back of the crewmember's knee. The response, called the Hoffmann reflex, is measured by recording the calf muscle contraction that results.
The Hoffmann reflex -a clinical method of measurement since the early 1800s -- is similar to another well known stretch reflex that is produced when a doctor taps your knee and your lower leg jerks. The more twitching there is, the more spinal cord excitability there is.
The goal of the experiment is to determine the change of spinal cord excitability, how rapidly it occurs and how long it continues after returning to Earth.
In the experiment, the muscle response is measured indirectly by an electromyogram - which measures the electrical activity in a contracting muscle. For a given stimulus, a resulting bigger muscle contraction implies more neurons fired, which in turn is indicative of higher spinal cord excitability.
To perform the experiment, crewmembers will participate in three test sessions: one at 24 hours after Shuttle launch; another between six and eight days into the Space Station mission; and one on the Space Station prior to the Shuttle's return to the Earth. Each session will take less than 60 minutes.The responses of the in-flight sessions, as well as of sessions after the mission, will be compared to responses measured before flight. The electrical shock the crew will receive will be comparable to the shock one receives from a static electricity shock.
Related experiments flew on eight previous Space Shuttle missions -- including STS-9, STS-41G, STS-61, STS-40, STS-42, STS-52, STS-58 and STS-78 -- and on Skylab.
Studies such as the H-Reflex experiment will enable researchers to better understand and assess the physiological risks of long-duration space flight and help them better prepare space crews for those flights. By knowing how a crewmember's body is affected in space, scientists can reduce the risk of acute and chronic health problems, increase productivity, and make the spacecraft more habitable.
Benefits from the H-Reflex study range from the obvious - potential improvement of crewmember health - to the less obvious - the potential for improving health care on Earth.
The H-Reflex study will provide information that will enable researchers to determine how much exercise is needed by crewmembers to maintain muscle mass and slow bone calcification.
For more information and photos on this experiment and other Expedition Two experiments, visit: